The present invention relates to an apparatus for the preparation of a solid or cellular plastic-forming, flowable reaction mixture from at least two flowable reaction components and at least one additional component. The apparatus broadly comprises supply vessels from which feed pipes for the reaction components lead via dosing pumps to a mix head, and a feed pipe for the additional component, which opens upstream of or into a pre-mixer having a stirrer shaft and being disposed in one of the feed pipes.
One device for mixing three components is described in U.S. Pat. No. 3,617,029.
Such apparatuses are utilized particularly in processing polyurethane systems, in order to add additional components to one or both principal components--generally a polyol and an isocyanate. Such additional components include activators, flameproofing agents, dye-pastes, low boiling point blowing agents and the like, such as are described in the "Kunststoff Handbuch" (Plastics manual), Vol. 7, Polyurethane, published by Carl Hanser Verlag, Munich, Vienna (1983), page 103. Other additives include explosive blowing agents, such as pentane, and fibrous and powdered additives. Such additives are added on conventional equipment via pre-mixers in the low-pressure region. A disadvantage of this is that unpleasant leakages can occur at the shaft sealings. Intermediate vessels are also frequently disposed downstream of the pre-mixers for interim storage of the mixture prior to processing. If the additional component is a blowing agent, this may volatilize into the gas space in the interim vessel. To avoid these disadvantages, it is advantageous to add the blowing agent on the high-pressure side. This is fundamentally known. Mix quality is, however, deficient when dosing is by means of static mixers. It is not, however, possible to utilize a high-performance mechanical stirrer on the high-pressure side, because there is no way of avoiding the necessity for a drive shaft lead through, because of the increased risk of leakage.
The object of the present invention was consequently to design the pre-mixer in an apparatus of the type noted in such a manner that it works without leakage and ensures the desired degree of mixing.